The present invention relates to an evaporated fuel processing device.
An evaporated fuel processing device disclosed in JP2005-155323A has a canister, a shutoff valve, and a purge passage. The canister includes an adsorbent material for adsorbing evaporated fuel generated in a fuel tank. The shutoff valve is provided in a vapor passage connecting the canister and the fuel tank. The purge passage connects the canister and an intake passage of an engine. While the engine is driven, a predetermined purge condition is satisfied. At this time, the negative intake pressure of the engine acts on the interior of the canister through the purge passage, with the interior of the canister communicating with the atmosphere. Air flows into the canister, and the evaporated fuel adsorbed by the adsorbent material is purged. The evaporated fuel is separated from the adsorbent material, and is guided to the engine through the purge passage. The shutoff valve is opened while the interior of the canister is being purged. As a result, pressure in the fuel tank is released.
The shutoff valve is opened when it receives an ON signal from an ECU, and is closed when it receives an OFF signal from the ECU. As a result, the flow rate of the gas flowing through the shutoff valve is adjusted, and pressure in the fuel tank is released. The shutoff valve is duty-ratio-controlled by the ON signal and the OFF signal. In the duty ratio control, the shutoff valve is periodically turned ON and OFF to repeatedly undergo a totally opened state and a totally closed state. Through this control, the average flow rate per unit time of the gas flowing through the shutoff valve is adjusted. Thus, it is rather difficult to perform fine adjustment of the flow rate of the gas flowing through the shutoff valve. Further, the pressure release precision for the fuel tank is rather low.
There has been a need for an evaporated fuel processing device capable of simple and easy control for precisely releasing pressure in the fuel tank.